Question

A layer of atmosphere that reflects medium frequency radio waves which is ineffective during night, is?
A. F layer
B. E layer
C. Stratosphere
D. Thermosphere

Answer 1

Recall the layer of atmosphere where ionization of electrons takes place. We have given that the layer which reflects the radio waves disappears at night. Therefore, find out which layers can be ruled out.

Complete step by step answer: Different layers of ionosphere affects the radio waves in different ways depending on the frequency of the radio waves. In the ionosphere, ionization takes place which varies with altitude. The different layers of the ionosphere are named as D, E and F layers.

The D region is present at the altitude between 60 to 90 km. The radiation between the D region is present only during the day and disappears at night. But the D layer does not reflect the radio waves noticeably.

The layer above the D layer is known as the E layer. The region of the E layer is present between 100 km to 125 km. The E layer reflects the radio waves of medium frequency. After the dark, the ionization falls quickly and the E layer disappears at night.

The layer above the E layer is known as the F layer. The region of the F layer is present around 300 km altitude. The F layer acts as a reflector for high frequency radio waves. Therefore, the option (A) is incorrect.

The layers stratosphere and thermosphere do not disappear at night like the ionosphere. Therefore, options (C) and (D) are incorrect.

So, the only correct answer is option (B).

Note: Since the region which reflects radio waves disappears at night, the layers stratosphere and thermosphere are out of the options. Students should remember the layers of atmosphere where the ionization of the signal took place due to sunlight.